# Submarine appears closer than it is

**Question**

When will the bomb hit the submarine? If an aeroplane flying 1200m above water, observes a submarine 1800m below it.

!!mu_"water"=4/3!!

- !!6sqrt(10)s!!
- !!20sqrt(5)s!!
- !!20s!!
- !!15s!!

**Solution**

This a simple question we just need to understand that the submarine appears closer to the pilot than it actually is.

!!"Real depth"/"Apparent depth"=mu!!

In our case, the submarine appears to be at !!600m!! below water level.

!!"Real depth"=4/3*600=800m!!

So the bomb has to travel a total of !!2000m!!.

Time taken !!sqrt((2h)/g)=sqrt(400)=20m/s!!